1. Field of the Invention
The present invention relates to a compact motor used for audio systems such as a mini disk (MD) player or a silent call device of mobile communications apparatuses, and more particularly, to an improved compact motor capable of being reflow-soldered so direct soldering on a printed wiring board is possible.
2. Description of the Related Art
Recently, technology for reflow-soldering of electronic parts to reduce the manufacturing cost has been rapidly developed. However, the reflow-soldering to a compact motor is not possible because of thermal demagnetization generated due to the heating of a built-in magnet. In particular, the problem of thermal demagnetization becomes serious when a high performance magnet inevitable for miniaturization of a system is used.
Since an operation point permeance coefficient is not high in a compact motor mounted in portable devices, thermal demagnetization cannot be avoided. In the case of a neodymium magnet showing great thermal demagnetization, reflow-soldering can not be performed at all. Also, it is not possible to use a magnet of having high coercive force showing less thermal deterioration because of high manufacturing costs.
To solve the above problems, it is an objective of the present invention to provide a compact motor capable of being reflow-soldered by solving the thermal demagnetization problem of a magnet with a simple structure.
Accordingly, to achieve the above objective, there is provided a compact motor capable of being reflow-soldered which is formed by installing a magnet in a housing, in which at least part of a surface where the magnet is installed is separated from a metal member forming part of the housing. Thus, even when the installation portion of the housing is reflow-soldered, because heat is not directly transferred, thermal demagnetization can be reduced.
It is preferred in the present invention that the magnet is an axial gap type and attached to a part of the housing by a double-sided adhesive sheet as a separating means. Since a double-side adhesive sheet exhibits a thermal insulation effect, transfer of heat to the magnet is difficult. Also, since the sheet is thin and it is not desired that operation point permeance coefficient is sacrificed, it is preferable that an axial gap type is used.
It is preferred in the present invention that the magnet is a radial gap type using a shaft as part of a magnetic path and is incorporated in the shaft through heat resistant resin as a separating means. Since the magnet can be separated from the shaft which is a metal member, transfer of heat to the magnet is difficult.
It is preferred in the present invention that the shaft is formed of stainless steel having a relatively low heat conductivity. Accordingly, a thermal insulation effect of stainless steel can be expected.
It is preferred in the present invention that at least the housing exposed to the outside air is formed of a stainless steel plate having a low heat conductivity. Accordingly, a thermal insulation effect of stainless steel can also be expected.
It is preferred in the present invention that the housing is covered so as not to be exposed directly to the outside air except for an installation portion or terminal to be reflow-soldered at a printed wiring board. Since more thermal insulation effect can be obtained, it is possible to cope with one of which the reflow time is quite long.
It is preferred in the present invention that a shielding portion for preventing transfer of heat to a main body of the housing is installed at the installation portion or terminal and the shielding portion is covered by heat resistant resin. Thus, heat conduction to the main body of the housing is reduced and the strength of the shielding portion can be covered by heat resistant resin.